An electrophotographic printer known in the art has drum cartridges respectively provided with photosensitive drums, and developer cartridges that supply toner to the corresponding photosensitive drums. One type of developer cartridge known in the art for use in this type of printer includes a developing roller for carrying toner, and a supply roller for supplying toner onto the developing roller.
Each developer cartridge includes an input gear into which an external drive force is inputted, a supply-roller gear for driving the corresponding supply roller by the drive force received from the input gear, and a developing-roller gear for driving the corresponding developing roller by the drive force transmitted from the input gear via the supply-roller gear. In other words, the drive force inputted into the input gear is transmitted to the developing-roller gear through the supply-roller gear.